The present invention relates to quartz crystal resonators and methods for making same. More particularly, the invention relates to surface mount quartz crystal resonators, and methods of making such resonators, which are straightforward in construction, inexpensive to manufacture, and effective and durable in use.
Quartz crystal resonators, because of their frequency accuracy and stability, are indispensable in modern electronics, for example, in telecommunications, computers, entertainment equipment and the like, as well as in other applications, many of which are well known. As used herein, a quartz crystal resonator, is a device comprising a piezoelectric quartz crystal element in the form of a thin plate, for example, a circular or rectangular plate, and an enclosure which can be sealed by some means to form a hermetic seal. Electrical terminals are provided which pass into the enclosure to provide the means to apply an alternating voltage across the quartz crystal element causing the element to vibrate. The piezoelectric quartz element has a set of thin conductive metallic electrodes deposited onto its major surfaces. The over lapping area of the electrode on one side of the plate with that of the electrode on the other side of the plate defines the resonating portion of the quartz element. The piezoelectric quartz crystal element resonates when the alternating voltage has the frequency of the resonant frequency of the quartz element, is applied. The resonant frequency of the quartz crystal element is determined by the piezoelectric and elastic constants of quartz, the dimensions of the quartz element, the metallic electrodes and other secondary factors.
Conventionally, surface mount quartz crystal resonators were made up of an electroded piezoelectric quartz crystal plate and a ceramic enclosure or base. The quartz crystal resonator plate is fixed in or on the ceramic enclosure by electrically conductive epoxy applied at two points on one end of the quartz crystal plate. A metal cover is welded to a metal flange on the ceramic enclosure. Alternately, a ceramic cover, is joined to the ceramic enclosure or base by means of adhesive or by reflow of low melting point glass.
The ceramic enclosures or bases are of laminated ceramic construction which employs a combination of cofired metallic depositions, metal vias and ceramic-to-metal seals. These ceramic components require a high level of technology to manufacture, are comparatively expensive, and have historically been in short supply.
It would be advantageous to provide surface mount quartz crystal resonators which are straightforward in construction, inexpensive to manufacture and effective and durable in use.
New surface mount quartz crystal resonators and methods for making same have been developed. The present resonators are straightforward in construction, relatively inexpensive to manufacture, effective in use, for example, in electronic equipment such as computers, handheld cell phones, wireless control and data transmission systems and the like, and do not rely on materials or components which have historically been in short supply. For example, the present surface mount quartz crystal resonators do not require, and preferably do not include, the ceramic enclosures or bases referred to above. Thus, the present invention avoids dealing with such ceramic enclosures or bases and the problems attendant thereto. Preferably, the present quartz crystal resonators are encapsulated in a base plate of quartz and a cover plate of quartz. Importantly, the present surface mount quartz crystal resonators when installed in the application circuit have substantial, preferably enhanced, resistence to shock and vibration. Also, the present resonators can be produced with a reduced height and/or profile relative to the resonators of the prior art. The present methods of producing surface mount quartz crystal resonators are straightforward to practice and provide a cost effective approach to producing surface mount quartz crystal resonators.
One important aspect of the present invention relates to resonator plates, which are a major component of the present quartz crystal resonators. In general, the present resonator plates comprise a quartz crystal-based plate or plate member including a central portion or region having a peripheral region, for example, around the width and length of the central portion. The central portion is adapted to resonate at a desired frequency, preferably in response to an alternating voltage being applied across the central region. A border or border portion is provided which substantially surrounds the peripheral region of the central portion. The border includes a first region physically separated or spaced apart from the central region, and a second region joined to the central portion.
In use, the central portion of the quartz crystal-based plate resonates at a desired frequency preferably in response to the application of an alternating voltage, while the border of the plate remains substantially stationary, as will be described hereinafter. Thus, only a portion of the quartz crystal-based plate resonates. The other portion, that is the border, of the plate is used to support the resonating central portion and to provide part of the housing or enclosure of the surface mount resonator.
The first region of the border which is physically separated from the central portion of the plate member preferably is formed by removal of quartz from a solid quartz crystal plate. In one embodiment, a solid quartz crystal plate is provided and a quantity of quartz is removed, for example, forming a slot, so that the first region of the border is spaced apart, for example, by the formed slot, from the resonating central portion.
The outer periphery of the quartz crystal-based plate may be of any suitable geometric shape, for example, suitable for use in a surface mount quartz crystal resonator. Particularly useful geometric shapes include a substantially circular shape, a substantially rectangular shape and the like. In one particularly useful embodiment, the quartz crystal-based plate has a rectangular outer periphery and includes a slot located between the central portion and the first region. The slot is located inwardly of the outer periphery along at least three sides of the rectangular outer periphery.
The central region of the quartz crystal-based plate preferably is provided with electrodes to facilitate the application of an alternating voltage. In one particularly useful embodiment, a first electrode is provided on the top surface of the central portion and a second electrode is provided on an opposing bottom surface of the central portion.
The thickness of the central portion may be substantially uniform or may be variable. In one very useful embodiment, the thickness of the central portion preferably is reduced in the region or regions of the central portion which are outside of the resonant region defined by the overlapping electrodes. For example, the thickness of the central region may be reduced in one or more regions of the central portion on which neither first nor second electrode is provided. This feature will be discussed in detail hereinafter.
In another very useful embodiment the thickness of the central portion is essentially uniform but is substantially or significantly reduced relative to the thickness of the border. This feature will be discussed in detail hereinafter.
In another broad aspect of the present invention, resonator assemblies are provided which comprise a quartz crystal-based plate or plate member, as described elsewhere herein, and a base plate secured to the plate so that the central portion of the plate is free to resonate relative to the base plate, for example, in response to an appropriate alternating voltage being applied thereto, across the plate. The base plate is secured to the border of the quartz crystal-based plate, preferably along substantially the entire outer portion of the border. This securement of the base plate to the border of the quartz crystal-based plate provides a substantially strong mechanical bond between the plate member and the base plate. This enhances the durability of the present resonators, for example, relative to the prior art resonators, which enhances the effective life of the present resonators.
Although the base plate and quartz crystal-based plate can be secured using various techniques, it is preferred that adhesives be employed. Thus, the assembly preferably includes an adhesive located between the base plate and the border of the quartz crystal-based plate. This adhesive is effective in securing the base plate to the border. A suitable adhesive may be employed. One particularly useful class of adhesives are epoxy-based adhesives.
Although the base plate may be comprised of any suitable material of construction, for example, metals, glasses, ceramics and the like, the preferred material of construction is quartz. The use of quartz is very effective in reducing costs while substantially matching the physical characteristics of the quartz crystal-based plate.
The base plate preferably includes a plurality of base electrodes positioned so that one base electrode is in electrical connection with the first electrode of the central portion of the plate member and another base electrode is in electrical connection with the second electrode of the central portion. Such base electrodes are very effective in providing the alternating voltage signal from a remote source to the resonating central portion of the plate member.
The electrodes described herein may be constructed of any suitable electrically conductive material. However, it is preferred that such electrodes comprise metals. The electrodes can be provided in any suitable manner. Preferably, the electrodes are provided by vacuum deposition onto the surface, as desired.
Quartz crystal resonators, in accordance with the present invention, include the quartz crystal-based plate and base plate, as described elsewhere herein, and, in addition, a cover plate secured to the quartz crystal-based plate so that the plate is located between the base plate and the cover plate. Preferably, the base plate and the cover plate are both secured to the border of the quartz crystal-based plate. More preferably, both the base plate and the cover plate are secured to substantially the entire outer portion of the border so that the resonator is firmly mechanically bonded together and the resonating central portion of the quartz crystal-based plate is hermetically sealed or enclosed.
In one embodiment, a first adhesive is provided which is located between the base plate and the border and is effective in securing the base plate to the border, and a second adhesive is provided and located between the cover plate and the border and is effective in securing the cover plate to the border. The compositions of the first and second adhesives may be the same or different, preferably the same.
Although any suitable material may be employed as the cover plate, the cover plate preferably comprises quartz. Thus, in one particularly useful embodiment, the quartz crystal-based plate, base plate and cover plate all comprise quartz. In one useful embodiment, at least one of the base plate and the cover plate includes an outwardly extending recess. This feature will be described in more detail hereinafter.
In another broad aspect of the present invention, methods for producing quartz crystal resonators are provided. Such methods include providing a solid quartz crystal plate. Quartz is removed from the solid quartz crystal plate to form a quartz crystal plate member including a central portion, a border and a space, preferably a slot, between the central portion and the border including a first region separated from the central portion and a second region joined to the central portion. First and second electrodes are placed on the top surface and the opposing bottom surface of the plate member, respectively. The plate member is secured to an electroded base plate so that the central region is free to resonate relative to the base plate, preferably in response to an alternating voltage being applied to the central region. The plate member is secured to a cover plate so that the plate member is located between the base and the cover plate.
In one embodiment, the base plate and the cover plate both comprise quartz and the securing steps include the use of adhesives to secure the plate member to the base plate and the plate member to the cover plate, respectively. The securing steps are effective to both mechanically bond the base plate, the plate member and the cover plate together, and form a hermetically sealed periphery. Electrically conductive adhesive, preferably electrically conductive epoxy adhesive, is employed to make contacts between the electrodes which are deposited on the central portion and the electrodes which are deposited onto the base plate which complete the electrical circuit of the resonator.
Each and every feature described herein, and each and every combination of two or more of such features, is included within the scope of the present invention provided that the features included in such a combination are not mutually inconsistent.
These and other aspects and advantages of the present invention are set forth in the following detailed description and claims, particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals.